Semantic portal
Geolocation
Geolocation
- Is used to get the geographical position of a user.
- Since this can compromise privacy, the position is not available unless the user approves it.
- Geolocation is most accurate for devices with GPS, like smartphone.
- Geolocation is also very useful for location-specific information, like: up-to-date local information, showing Points-of-interest near the user, turn-by-turn navigation (GPS).
Using HTML Geolocation
//the example below returns the latitude and longitude of the user's position
<script>
var x = document.getElementById("demo");
function getLocation() {
if (navigator.geolocation) {
navigator.geolocation.getCurrentPosition(showPosition);
} else {
x.innerHTML = "Geolocation is not supported by this browser.";
}
}
function showPosition(position) {
x.innerHTML = "Latitude: " + position.coords.latitude +
"<br>Longitude: " + position.coords.longitude;
}
</script>The getCurrentPosition() method is used to return the user's position.
Handling Errors and Rejections
function showError(error) {
switch(error.code) {
case error.PERMISSION_DENIED:
x.innerHTML = "User denied the request for Geolocation."
break;
case error.POSITION_UNAVAILABLE:
x.innerHTML = "Location information is unavailable."
break;
case error.TIMEOUT:
x.innerHTML = "The request to get user location timed out."
break;
case error.UNKNOWN_ERROR:
x.innerHTML = "An unknown error occurred."
break;
}
}The second parameter of the getCurrentPosition() method is used to handle errors. It specifies a function to run if it fails to get the user's location.
Displaying the Result in a Map
//in the example below, the returned latitude and longitude is used to show the //location in a Google Map (using a static image)
function showPosition(position) {
var latlon = position.coords.latitude + "," + position.coords.longitude;
var img_url = "https://maps.googleapis.com/maps/api/staticmap?center=
"+latlon+"&zoom=14&size=400x300&sensor=false&key=YOUR_:KEY";
document.getElementById("mapholder").innerHTML = "<img src='"+img_url+"'>";
}To display the result in a map, you need access to a map service, like Google Maps.